Method of effecting a smooth surface finish on cast iron objects

ABSTRACT

A METHOD OF SURFACE FINISHING OBJECTS MADE OF CAST IRON HAVING A MICROSTRUCTURE WHICH CONTAINS SEPARATED GRAPHITE IN NON-LAMINAR FORM LIQUEFIED BY A GAS-OXYGEN FLAME AFTER WHICH A STREAM OF GAS CONSISTING ESSENTIALLY OF OXYGEN IS BLOWN ONTO SAID SURFACE TO FORM AN OXIDE SLAG WHICH IS AFTERWARDS REMOVED.

Sept. 25, 1973 s ET AL 3,761,321

METHOD OF EFFECTING A SMOOTH SURFACE FINISH ON CAST'IRON OBJECTS Filed April 6, 1971 igf ik 3,761,321 METHOD OF EFFECTING A SMOOTH SURFACE FINISH N CAST-IRON OBJECTS Damjan Schmit, 1 Rue Nicolaus Welter, Luxembourg, Germany, and Egon Evertz, 23 Vorlaunder Strasse, 565 Solingen, Germany Filed Apr. 6, 1971, Ser. No. 131,693

Int. Cl. C2111 1/00 US. Cl. 148-95 2 Claims ABSTRACT OF THE DISCLOSURE A method of surface finishing objects made of cast iron having a microstructure which contains separated graphite in non-laminar form wherein the material of the surface to be treated is first liquefied by a gas-oxygen flame after which a stream of gas consisting essentially of oxygen is blown onto said surface to form an oxide slag which is afterwards removed.

This invention relates to a method for providing a smooth surface finish on objects formed of cast iron having a microstructure which contains separated graphite in non-laminar form. Examples of such cast-iron are the so-called white solidifying types of cast iron, especially those having 45-50% carbon and at the most 1% silicon and 1-6% maganese. Other examples are cast irons in which the graphite exists in spheroidal form.

Objects made of such cast-iron often require surface finishing and this may be effected by abrading the surfaces of the objects. This is for instance desirable when casting flaws (which would be unacceptable in use) are present in said surfaces. Furthermore such surface finish ing is also necessary when the cast surfaces show defects of any kind after use, for instance heat cracks arising under the influence of heat as may occur with rollers in rolling mills or with iron moulds in steel Works. Moreover, surface finishing may also be carried out when the geometrical shape of the surface has to be altered for some reason, such as for instance when one has to level a surface rendered non-planar by the influence of the heat.

Surface finishing in this way has so far been carried out mechanically in different ways, for instance by milling or by grinding. In practice, these expensive methods have the disadvantage that the surface, formed by solidification from the molten phase, is completely lost in situations where it is regarded as especially advantageous to retain it.

Finishing methods involving fusion cannot be carried out on objects of the previously mentioned kind since it is known that the white solidifying types of cast iron cannot be welded, while considerable stresses arise during the heating of the types of cast iron having spheroidal graphite.

The considerable stresses which lead to cracks in the above-mentioned types of cast iron, after heating and cooling processes can be seen from the following chart:

Chemical composition ('71,) Stress (kg/mini) C S1 Mu P S 1 2 3 Structure 0.004 6.4 0.6 12.6 Pearlite plus spheroibite dalgrap 0.003 5.5 0.4 10.9 Pearlite plus 40% ferrite plus spheroidal graphite.

0.1 3.3 Pearlitepluslaminated graphite.

0.4 11.3 Pearlite plus ferrite (steel).

United States Patent O ice to formation of cracks are further especially high in the case of cast objects which are thermally stressed in use such as for instance iron moulds in steel work and which can be seen from the following chart:

The object of the present invention is to provide an improved method of surface finishing objects made of cast iron having a microstructure which contains separated graphite in non-laminar form.

In accordance with the invention there is provided a method of surface finishing objects made of cast iron having a microstructure which contains separated graphite in non-laminar form characterized in that the cast object in a cold condition is first of all heated on the surface which is to be treated by a gas-oxygen flame so as to liquefy material on said surface and is then treated further with a stream of gas essentially consisting of oxygen in such a way that an oxide slag is formed on the liquefied material, said slag being afterwards removed.

Such method is especially successful when applied to objects having thick walls such as iron moulds in steel works. Either white solidifying types of cast iron with 4.0 to 5.0% carbon and at most 1%- silicon and 1 to 6% maganese, or types of cast iron having spheroidal graphite can be treated in this way.

It is essential with the method according to the invention that the cast iron objects are treated without preheating as distinct from a known method (the so called flame planing or machining) in which the objects, such as steel ingots or steel slabs, are heated up to temperatures of several hundred degrees centigrade before being treated in order to avoid stress cracks in the region of the flame-planing. This treatment requires a considerable expenditure of energy and time and can only be carried out on geometrically simple bodies.

The present invention however, wherein the cast objects are treated when initially cold, permits a very even surface abrasion even with complex cast objects, especially iron moulds in steel works. Moreover, the treated surface has a structure which is very similar to the especially advantageous original skin of the casting. This advantage is maintained even when the treated surface according to the invention is later subjected to a minor mechanical finishing operation.

One example of a method according to the present invention will now be described with reference to the accompanying drawing which is a perspective view of an object having a surface which is to be treated by the method.

Firstly an object such as is shown in the drawing is taken in the cold condition and the surface (indicated by reference numeral 6 in the drawing) is heated by a gas-oxygen flame such as an acetylene-oxygen flame which may be produced from a plurality of nozzles (s ay from 8-15 nozzles) arranged in an annulus, each of said nozzles being about one-half mm. in diameter and being arranged so that the acetylene-oxygen mixture issues from the nozzles at a pressure of about 1.5 atmospheres.

Said nozzles are conveniently arranged to surround a central nozzle through which oxygen can be passed after the acetylene-oxygen flame has liquefied the surface 6. The central nozzle may have a diameter of from 8-15 mm. (such as -12 mm.) and in use the oxygen is fed to said central nozzle under a pressure of from 8-40 atmospheres although the best results appear to be obtained by using oxygen pressures of between 1540 atmospheres. After liquefying of the surface 6 has taken place by the acetylene-oxygen flame, the application of the stream of oxygen will result in the formation of a slag which is afterwards removed in any convenient manner.

Preferably the finishing of the surface in question is effected by first of all treating one of the smaller edges of the surface such as that indicated by reference numeral 1 in the drawing. Afterwards treatment proceeds in paths at right angles to the first treated edge such paths defining relatively narrow bands taken alternately from opposite sides of the surface and working inwardly from the longer outer edges thereof. Thus with reference to the drawing, after having treated the edge 1 the band indicated by reference numeral 2 is next treated, followed by band 3, band 4, band 5 and so on until the whole area of surface 6 is treated by first liquefying and then applying oxygen to form a slag which is later removed, all as above de scribed.

The above described method applied to a rectangular surface can also be applied to a curved surface such as for example a cylindrical surface. In the latter case one of the circular edges of the cylindrical surface can first of all be treated following which treatment is completed by applying the flame and then the oxygen blast successively along relatively narrow axially extending bands which are approximately diametrically opposite to each other until the whole of the cylindrical surface to be treated has been covered. Such a method would for ex- 4 ample be suitable in treating the outer surface of a roll or the inner surface of an iron mould.

What is claimed is:

1. A method of surface finishing objects made of cast iron having a microstructure which contains separated graphite in non-laminar form characterised in that the cast object in a cold condition is first of all heated on the surface which is to be treated by a gas-oxygen flame to a temperature suflicient only to liquely material on said surface and is then treated further with a stream of gas essentially consisting of oxygen in such a way that an oxide slag is formed in the liquefied material, said slag being afterwards removed.

2. A method according to claim 1 characterized in that the surface finishing is first of all undertaken along the smallest edge of the surface and proceeds from there in paths which run at right angles to said edge, said paths comprising narrow bands which alternate successively from opposite sides of the object starting from the outer edges thereof and finishing in the centre of the surface.

References Cited UNITED STATES PATENTS 3,322,578 5/1967 Thompson 148-95 3,455,747 7/1969 Lytle 1489.5 3,508,323 4/1970 Richards 148-9 3,354,002 11/1967 Gingerich et al. 148-95 3,436,276 4/ 1969 Thompson 1489.5 3,231,430 l/1966 Krieger et a1. 1489.5 2,290,295 7/1942 Scheller 1489.5

WAYLAND W. STALLARD, Primary Examiner UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNU. 3,761,321

DATED September 25, 1973 INVENTUR(S): Damjan Schmit and Egon Evertz It is certified that error appears in the aboveidentified patent and that said Letters Patent is hereby corrected as shown below:

On the Title Page add:

Assignee: Tent Societe Anonyme Signed and Sealed this Fifth Day of April, 1988 Arrest:

DONALD J. QUIGG Artesting Officer Commissioner of Patents and Tradenmrks 

